This invention relates generally to linear actuators and more particularly concerns linear actuator which provides regulated speed displacement regardless of the magnitude of the load.
Many presently known linear actuators employ dual drive systems. Typically, a pneumatic or hydraulic system is combined with a screw system which may be pneumatically, hydraulically or electrically driven. In some applications, both drive systems are used as load actuators with one system backing up the other in case of failure. In other applications, the systems simultaneously actuate the load. Either way, both drive systems affect the force applied to the load but none utilize these drive systems for the sole purpose of regulating the output speed of the actuator.
The efficiency and life of these actuators is further limited because the operating force overly exceeds the magnitude of the load and the difference is absorbed by the actuator components. Some dual systems counterbalance forces to hold this differential at a minimum, but then speed control suffers.
It is, therefore, an object of this invention to provide a dual drive linear actuator in which one drive system determines the force delivered to the load and the other drive system determines the speed of the load without varying the force delivered to the load. It is a further object of this invention to provide a dual drive linear actuator in which force is applied to the load by a pneumatic or hydraulic drive system while the speed of the load is independently controlled by a screw in a hydraulic, pneumatic, electric or clock driven system. Another object of this invention is to provide a dual drive linear actuator in which the extension and retraction speeds of the load do not vary as a consequence of the magnitude of the load. It is also an object of this invention to provide a dual drive linear actuator which is capable of holding the load in midstroke. And it is an object of this invention to provide a dual drive linear actuator in which the speed control system experiences no significant torque, even with a load of greatest magnitude.